1. Tacit difference in upbringing of children for different roles between high and low socio-economic-classes (SEC); low SEC tend to provide punitive and stressful environment damaging pre-frontal cortex, while high SEC providing discussion with better vocabulary and information content
2. Society's treatment towards different classes
3. Migration pattern of races
4. Medical care between classes
5. Nutritional differences (vitamins, breast-feeding amounts to ~ 6 point IQ difference) between food taken by different classes

Nisbett also points that probably hereditary arguments also address non-trivial part of genetics, things like gene linked to happiness and rewards. He writes about Moore's research "When the child was having trouble with a design, white adoptive mothers tended to diffuse tension by joking, grining, and laughing."

However i did get confused reading "The black adoptive mothers were more likely to frown and scowl. The white adoptive mothers encouraged the problem-solving efforts of their children (“Gee, that’s an interesting idea” or “You’re good at this”). Black mothers were more likely to express disapproval (“You know that does not look right” or “You could do better than this if you really tried”)." from Nisbett while Lareau writing "The working-class and poor parents viewed children's development as spontaneosly unfolding, as long as they were provided with comfort, food, shelter, and other basic support. This commitment, too, required ongoing effort; sustaining children's natural growth despite formidable life challenges is properly viewed as an accomplishment.".